This invention relates to a method and apparatus for the microwave heating of flowable materials, and in particular to the devulcanization of particulate rubber scrap.
More particularly, the present invention provides a system including a method and apparatus for the uniform microwave heatinng of flowable materials to high temperatures in a controlled atmosphere isolated from the environment. The present invention finds particular application in the processing of scrap vulcanized rubber into at least partially devulcanized form by microwave heating. It has been known for some time that such scrap rubber can be subdivided into particulate form and reused after being devulcanized by the application of microwave energy. However, the application of this technique has been limited because of the inability to find a suitable method and apparatus by which the same can be scaled to the processing of significant quantities of such rubber. Rubber is particularly difficult to process in microwave fields since rubber at room temperature is relatively non-conductive but becomes progressively more conductive at elevated temperatures. What this means is that the application of a microwave field to reacted heating to elevated temperatures adequate to cause devulcanization of any particulate or elemental portion of rubber also creates a significantly higher conductivity in that portion which in turn results in a run-away thermal condition in which the particle which has achieved such an elevated temperature absorbs an undue share of the microwave energy present ultimately becoming so overheated that it bursts into flame. Accordingly, attempts to reprocess previously vulcanized rubber by conveyor belt transportation of same through a microwave oven have not been commercially successful. There is, therefore, a need for a new and improved method and apparatus for the devulcanization of rubber scrap which will overcome the foregoing limitations and disadvantages.
In addition to the foregoing there are a number of other microwave heating applications in which it would be desirable to process a flowable material passing through a microwave oven in a continuous process which material it is desired to maintain in a state of isolation from the environment. Heretofore, there has not existed a suitable conveying system for processing such materials.
There is, therefore, a need for a general conveying system by which flowable material may be continuously processed, and heated or reacted in a microwave oven while in an agitated state and in isolation from ambient atmosphere.